The present invention relates generally to devices used with photographic equipment, and more specifically to an automatically controlled electronic flash device used as an artificial source of light necessary to illuminate photographic objects.
Automatically controlled electronic flash devices have heretofore been used as a source of artificial light. In such prior devices a predetermined amount of light is produced from an electronic flash tube. The amount of light is automatically adjusted in accordance with the output of a light measuring device used to represent the distance from a camera to a photographic object. One such prior art device is for example shown in published Japanese Utility Model No. Sho 49-148052. The device disclosed in the Japanese publication relates to an automatically controlled electronic flash device which permits a selection between two aperture openings to be set on a camera for a film having a particular speed or sensitivity. The device is provided with a calculator having a pair of neon tubes used to indicate the aperture setting (f-number) which is representative of the aperture to be set on the camera, as well as the maximum permissable distance or range from the camera to the photographic object. In this prior device indicia is used to represent the distance between the camera and the object. Similarly indicia representing the f-number (aperture setting) is also used. The f-number indicia are movable with respect to the distance setting indicia and also movable relative to the two neon tubes depending upon the setting of a particular film speed or sensitivity. The neon tubes are selectively lit depending upon the position of a manual switching member. When the manual switching member is set to a first position and a certain film sensitivity or speed is set, a particular combination of aperture setting and maximum permissable distance between the camera and the object is indicated by one of the neon tubes being lit. When the manual switching member is set to a second position, with the same film speed or sensitivity being set, another combination of aperture setting and maximum permissible distance between the camera and the object is indicated by the other neon tube being lit. The use of the neon tubes or lamps provides the operator, or photographer, with the ability to see the selected aperture setting and maximum permissable distance between the camera and the object even when using the device in the dark.
The disadvantage of this prior device, however, relates to the fact that the neon tubes are connected to opposite terminals of a capacitor used for storing electric charge to energize a flash tube. Accordingly, the neon lamps cannot be lit unless the potential across the capacitor reaches a level sufficient to allow the flash tube to emit a sufficient quantity of light. In other words, unless the capacitor is fully charged the combination of proper aperture setting to be chosen on the camera and the maximum permissable distance between the camera and the object for a particular film speed, cannot be indicated. Therefore, soon after the flash tube has reached a condition for emitting light, imaging using the flash as a source of artificial light may not be possible.
It is accordingly an object of the present invention to provide an improved automatic electronic flash device which overcomes the disadvantages of the prior art.
It is a more specific object of the present invention to provide an automatic electronic flash device which provides for the selection of a particular aperture size to be set on a camera for any selected film speed, and which, independent of the condition of charge on the capacitor used to fire the flash tube, indicate the aperture size to be set on the camera and the maximum permissable distance between the camera and the object which is available under the conditions for the selected film speed and a set aperture size.